The use of diuretics has become a known strategy in attempts to subvert urine drug testing. These substances increase the body’s fluid excretion, which is intended to lower the concentration of drug metabolites present in a urine sample. The core premise is not that diuretics mask the drug itself, but rather that they dilute the specimen to a degree that the drug traces fall below the laboratory’s detection threshold. This action alters the sample’s natural chemical balance, leading to a classification of the sample as dilute.
How Diuretics Cause Sample Dilution
Diuretics work by disrupting the kidney’s normal fluid regulation process, forcing the body to excrete an abnormal volume of water and electrolytes. Many diuretics act on the renal tubules, such as the Loop of Henle, where they inhibit the reabsorption of sodium and chloride. This inhibition prevents water from following the electrolytes back into the bloodstream, which significantly increases the volume of urine produced. The increased water content in the urine drastically lowers the concentration of all dissolved substances, including the metabolic byproducts of any drugs consumed. Simultaneously, this process flushes out natural concentration markers that laboratories use to validate the sample.
Identifying Diluted Urine Samples
Laboratories routinely employ specific validity checks on every urine sample to ensure the specimen has not been diluted. The primary marker used to detect dilution is the measurement of creatinine, a waste product of muscle metabolism that is normally excreted at a relatively stable rate. Undiluted urine typically contains creatinine levels well within a predictable range, generally between 20 and 300 milligrams per deciliter (mg/dL). If a sample’s creatinine level falls below a specific threshold, most commonly 20 mg/dL, it is immediately flagged as a dilute specimen.
Specific Gravity
The second critical check is the measurement of specific gravity, which determines the concentration of dissolved particles like salts and minerals in the urine compared to pure water. Normal urine has a specific gravity range of approximately 1.003 to 1.030. A reading that is too low, often falling between 1.001 and 1.003, suggests the presence of excessive water content. When a sample exhibits both low creatinine and low specific gravity, the laboratory confirms the sample is dilute, indicating that the concentration of drug metabolites may not accurately reflect the donor’s actual body levels.
Outcomes of Submitting a Dilute Sample
When a urine specimen is officially flagged as dilute, the result is typically classified as “invalid” or “negative dilute,” even if no drug metabolites were detected above the cut-off level. This classification means the sample’s integrity is compromised, and the test cannot confirm the absence of drug use. The administrative response to a dilute sample is almost always a mandatory re-test under stricter supervision.
In the context of employment or probation testing, a dilute result is often treated with high suspicion because it suggests a deliberate attempt to interfere with the testing process. For a first-time “negative dilute” result, an employer or monitoring program will usually require a re-test, often with very little notice to prevent excessive water consumption. However, if a sample is classified as “positive dilute,” meaning drug traces were found even with the dilution, the test is treated as a confirmed positive result. Repeated dilute results, particularly in monitoring programs, can sometimes be treated as equivalent to a failed test, as the individual is viewed as non-compliant with the testing requirements.